Japan once ran out of instances of a type we wanted. When we finally got more, they all got located on the same host (without us knowing)... that host went down and we lost more VMs of a distributed database than we would have liked.
I've read that there are even regional differences in S3 metadata (like hash values for the file ... useful for seeing if you have the same file and don't need to upload and get dinged by AWS's ludicrous I/O costs).
AWS was also kind of scummy with the retirement of... I think it was us-east-1e where they have no m5s. We had to move AZs for one of our databases and so the AZ name of that rack of servers no longer was the same as the actual AZ. We eventually fixed it, but why AWS couldn't transparently migrate an AZ?
Anyway, the magic cloud isn't as magic as it appears. You'll run into edge cases.